Such a gripper is known from EP-A-0 482 406. In the known gripper the control means for controlling the carrying strips are formed by two piston/cylinder-assemblies 63 which are connected to the carrying strips via operating plates 33, 34 which operating strips are hingedly connected to the carrying strips. The control means for controlling the movement of the gripper leaves is performed by two piston/cylinder-assemblies 56, 57. As is clear from FIG. 5 of EP-A-0 482 406, the operating plates 33, 44 are positioned between the article and the gripper leaves. In view of the fact that the gripper leaves have to absorb the forces which are exerted by the operating plates on the carrying strips, the gripper leaves have to be strong and, consequently, the gripper leaves are rather thick, especially, in the upper region where the moment of force exerted by the piston cylinder-assemblies 56, 57 is large. Due to the interposition of the operating plates between the box to be carried and the gripper leaves and due to the thickness of the gripper leaves, there must be left space around the box which is handled by that gripper. It should be noted that the known gripper is not especially intended for placing objects in overpack boxes. The known gripper is intended for placing boxes on pallets.
A gripper for placing egg boxes in overpack boxes in which the egg boxes are fittingly received is known from, for instance, European patent application EP-A-0 666 149. The gripper leaves are therefore of slender design so that they can move through the narrow space between an egg box and the relevant overpack box. The known gripper is particularly intended for lifting egg boxes which themselves have a certain rigidity. Egg trays are considerably weaker and therefore need more support. Moreover, the known gripper is intended for gripping one or a number of egg boxes which are at the same level. The known gripper is explicitly not suitable for gripping a stack of egg trays.
The filling of overpack boxes with stacks of egg trays has hitherto been done manually. The trays are stacked up by rotating them alternately through 90 degrees. In general, a person lifts two stacked trays manually and places the trays on the bottom of an overpack box. Subsequently, this operation is repeated two times for an overpack box in which one stack is contained and five times for an overpack box in which two stacks are contained. This packaging process requires a number of difficult repeating movements, which are not only monotonous to the packaging personnel, but which can also lead to overburdening injuries in the forearm, wrist and/or hand. The gripper according to the present invention has for its object to automatize this process, so that by one single movement one or two stacks of trays can be placed in an overpack box.